Re: [PATCH] x86/shadow: account for ioreq server pages before complaining about not found mapping

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 29/04/16 09:13, Jan Beulich wrote:
> prepare_ring_for_helper(), just like share_xen_page_with_guest(),
> takes a write reference on the page, and hence should similarly be
> accounted for when determining whether to log a complaint.
>
> This requires using recursive locking for the ioreq server lock, as the
> offending invocation of sh_remove_all_mappings() is down the call stack
> from hvm_set_ioreq_server_state(). (While not strictly needed to be
> done in all other instances too, convert all of them for consistency.)
>
> At once improve the usefulness of the shadow error message: Log all
> values involved in triggering it as well as the GFN (to aid
> understanding which guest page it is that there is a problem with - in
> cases like the one here the GFN is invariant across invocations, while
> the MFN obviously can [and will] vary).
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

IMO, this is a 4.7 candidate. I already had a TODO list item of working
out why the shadow code was always complaining.

Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>, albeit with one
further suggestion.

> --- a/xen/arch/x86/mm/shadow/common.c
> +++ b/xen/arch/x86/mm/shadow/common.c
> @@ -35,6 +35,7 @@
>  #include <asm/current.h>
>  #include <asm/flushtlb.h>
>  #include <asm/shadow.h>
> +#include <asm/hvm/ioreq.h>
>  #include <xen/numa.h>
>  #include "private.h"
>  
> @@ -2591,7 +2592,8 @@ int sh_remove_write_access_from_sl1p(str
>  /* Remove all mappings of a guest frame from the shadow tables.
>   * Returns non-zero if we need to flush TLBs. */
>  
> -static int sh_remove_all_mappings(struct domain *d, mfn_t gmfn)
> +static int sh_remove_all_mappings(struct domain *d, mfn_t gmfn,
> +                                  unsigned long gfn)

It would be nice if we could use gfn_t rather than having more unsigned
longs.

~Andrew

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